Cryptosporidium is an apicomplexan parasite capable of infecting a variety of animals, including humans. One particular species, Cryptosporidium parvum, is a coccidian parasite that poses particular threat to humans by causing gasteroenteritis in immuno-competent adults and infants, and occasionally life-threatening diarrhea in immuno-deficient individuals, such as infants, the elderly and AIDS patients. The mortality rate in AIDS patients infected with Cryptosporidium parvum is as high as fifty percent. Transmission of Cryptosporidium parvum is direct, by the fecal-oral route or by contamination of water supplies, swimming pools, and untreated surface water. Able to infect with as few as 30 microscopic oocysts, Cryptosporidium parvum is considered a leading cause of persistent diarrhea in developing countries and is a major threat to the U.S. water supply.
Cryptosporidium parvum exists in nature as a thick walled oocyst that is extremely resistant to environmental factors, exhibiting the ability to survive for months in the environment if maintained in a cool and moist setting. The oocysts are highly resistant to conventional chlorination of drinking water and their size presents a problem for water filtration systems typically employed by municipal water authorities. In fact, Cryptosporidium parvum oocysts are so robust that they are able to maintain their integrity and viability after a 24 hour exposure to full strength bleach. Their resistance to destruction by environmental and chemical means is particularly alarming since nearly ninety percent of all raw water supplies are infected with Cryptosporidium parvum oocysts.
In the United States, the method currently approved by the Environmental Protection Agency for detecting Cryptosporidium parvum is an antibody staining method referred to as “Method 1622”. This method has several drawbacks, including the subjectivity of the assay, high antibody background resulting in an unacceptable number of false positives, and its labor intensive aspects, requiring hours of microscopic analysis. Other methods currently available for detecting Cryptosporidium parvum, including detection of genomic DNA by the polymerase chain reaction (PCR) and immunological assays such as the enzyme-linked immunosorbent assay (ELISA), have significant sensitivity and specificity problems. Thus, a need exists for a sensitive and specific assay which can be used to determine the presence of Cryptosporidium organisms, and Cryptosporidium parvum in particular, in a test sample, as well as a method for releasing the contents of the thick walled oocysts.